Self expanding stent

ABSTRACT

A self expanding stent ( 10 ) formed from a resilient wire. The resilient wire comprises a zig zag form including an odd number of struts ( 12 ) such as seven struts and a bend ( 14 ) between each strut. There is first loop ( 18 ) of the resilient wire at the terminal end of a first strut and a second loop ( 18 ) of the resilient wire at the terminal end of a last strut. The stent as formed is substantially planar but in use is formed into a substantially cylindrical form ( 20 ) by being stitched onto a tubular body of a biocompatible graft material with at least the first strut and the last strut overlapping.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of provisional application Ser. No.60/759,851, filed Jan. 18, 2006 and is a continuation of non-provisionalapplication Ser. No. 11/654,423.

TECHNICAL FIELD

This invention relates to a stent and more particularly to a selfexpanding stent used in endovascular therapies.

BACKGROUND OF THE INVENTION

Self expanding stents are used either bare or in conjunction with abiocompatible graft material in endovascular therapies in which thestent is placed in a body lumen to reinforce the lumen or a tubulargraft placed into the lumen.

Self expanding stents are generally formed from a resilient wire such asNitinolJ or stainless steel and made in a zig-zag form with the endsjoined to form a cylindrical or polygonal body. The cylindrical orpolygonal body can be reduced in diameter by compressing the stentagainst its resilient forces to permit placement by endovasculartechniques and then released to expand in a desired position in thevasculature. The joining of the ends of the resilient wire can be aproblem because joining requires welding or soldering and the heatinginvolved can induce brittleness around the joint.

NitinolJ in particular, is difficult to join and the region around thejoint may need to be annealed which could remove the resilient nature ofthe material. This invention proposes an alternative method of formingself expanding stents and a stent so formed or at least provides apractitioner with a useful alternative.

Throughout this specification the term distal with respect to a portionof the aorta, a deployment device or a prosthesis is the end of theaorta, deployment device or prosthesis further away in the direction ofblood flow away from the heart and the term proximal means the portionof the aorta, deployment device or end of the prosthesis nearer to theheart. When applied to other vessels similar terms such as caudal andcranial should be understood.

SUMMARY OF THE INVENTION

In one form therefore the invention is said to reside in a selfexpanding stent comprising a resilient wire, the resilient wirecomprising a plurality of struts and a bend between each strut, thestent as formed being substantially planar and in use being able to beformed into a substantially cylindrical form with at least the firststrut and the last strut overlapping.

Preferably the self expanding stent comprises a first loop of theresilient wire at the terminal end of the first strut and a second loopof the resilient wire at the terminal end of the final strut. The loopspreferably comprise at least one and a quarter turns of the resilientwire.

There may be an odd number of struts such as the stent comprising sevenstruts and six bends.

Alternatively there can be an even number of struts and at least twostruts overlapping when the stent is formed into the substantiallycylindrical form.

The resilient wire can be selected from the group comprising NitinolJ,stainless steel, cobalt alloys and titanium alloys.

The stent is formed into its cylindrical form by being stitched onto atubular body of a biocompatible graft material with at least the firststrut and the last strut overlapping.

In an alternative form the invention resides in a self expanding stentcomprising a resilient wire, the resilient wire comprising a zig zagform including plurality of struts and a plurality of bends, a bendbetween each strut, a first loop of the resilient wire at the terminalend of the first strut and a second loop of the resilient wire at theterminal end of the last strut, the stent in use being able to be formedinto a substantially cylindrical form with the first strut and the laststrut overlapping.

In an alternative form the invention resides in a self expanding stentcomprising a resilient wire, the resilient nitinol wire comprising a zigzag form including seven struts and a bend between each strut, a firstloop of the resilient wire at the terminal end of a first strut and asecond loop of the resilient wire at the terminal end of a last strut,the stent in use being formed into a substantially cylindrical form bybeing stitched onto a tubular body of a biocompatible graft materialwith at least the first strut and the last strut overlapping.

It will be seen that by this invention there is provided a selfexpanding stent which when mounted onto a tubular body of graft materialcan be made into the desirable cylindrical form but does not have anywelded joint which reduces the chance of fracture caused byembrittlement which may occur during welding or soldering. This isparticularly desirable for NitinolJ wire.

BRIEF DESCRIPTION OF THE DRAWING

This then generally describes the invention but to assist withunderstanding reference will now be made to the accompanying drawingswhich show various embodiments of the invention. In the drawings:

FIG. 1 shows one form of stent as formed according to the presentinvention;

FIG. 2 shows a perspective view the embodiment of FIG. 1 formed into acylindrical self expanding stent;

FIG. 3 shows a plan view of the embodiment of FIG. 2;

FIG. 4 shows an alternative form of stent as formed according to thepresent invention;

FIG. 5 shows a perspective view of the embodiment of FIG. 4 formed intoa cylindrical self expanding stent;

FIG. 6 shows a plan view of the embodiment of FIG. 4;

FIG. 7 shows a connection socket incorporating a stent according to thepresent invention; and

FIG. 8 shows a side branch stent graft or prosthesis of the type adaptedfor deployment into the iliac arteries and including a connection sockethaving a stent according to this invention.

DETAILED DESCRIPTION

Now looking at the drawings and more particularly the first embodimentof stent according to the present invention shown in FIGS. 1 to 3.

The stent 10 is formed from a resilient wire such as NitinolJ wire orstainless steel and comprises a plurality of struts 12 with a bend 14between each pair of struts 12. In this embodiment there are sevenstruts 12 and six bends 14 between them. The terminal struts 16 at eachend terminate in a loop 18 which comprises at least one turn of theresilient wire and preferably one and a quarter turns. The use of theloops 18 prevent sharp ends from the wire stent from digging into thevasculature into which a stent graft, incorporating the self expandingstent of the present invention, is deployed. As formed the struts, bendsand loops are in a single plane and when they are to be used they areformed into a cylindrical or polygonal body 20 as shown in FIG. 2. Inthe cylindrical form the terminal struts 16 overlap each other to givein effect an at least one strut overlap. When there are an odd number ofstruts then the terminal loops 18 are positioned at the opposite ends ofthe cylindrical or polygonal body 20.

The embodiment shown in FIGS. 1 to 3 has seven struts 12 and six bends14 between them and hence when formed into cylindrical or polygonal body20 has a plan view in the shape of a hexagon as can be seen in FIG. 3.

When assembled onto a stent graft the stent is maintained into itscylindrical or polygonal body form by being stitched to the tubular bodyof the graft material.

NitinolJ is a shape memory metal formed from a nickel-titanium (NiTi)alloy that “remembers” its geometry. The wire is formed into the desiredzig-zag shape and then heat treated to retain that shape. After cooling,if it is deformed, it will return to the desired zig-zag shape.

Now looking at the alternative embodiment of stent according to thepresent invention shown in FIGS. 4 to 6.

The stent 30 is formed from a resilient wire such as NitinolJ wire orstainless steel and comprises a zig zag structure formed from aplurality of struts 32 with a bends 34 and 35 between each pair ofstruts 32. In this embodiment there are twelve struts 32, five bends 34at one side of the zig-zag structure and six bends 35 at the other sideof the zig-zag structure between them. The terminal struts 36 at eachend terminate in a loop 38 which comprises at least one turn of theresilient wire and preferably one and a quarter or more turns. The useof the loops 38 prevent sharp ends from the wire stent from digging intothe vasculature into which a stent graft, incorporating the selfexpanding stent of the present invention, is deployed. As formed thestent comprised of struts, bends and loops is in a single plane and whenit is to be used it is formed into a cylindrical or polygonal body 40 asshown in FIG. 5. In the cylindrical form the struts are overlapped eachother to give a two strut overlap. As there is an even number of strutsthen the terminal loops 38 are positioned at the same end of thecylindrical or polygonal body 20. FIG. 5 also shows that when the stentis formed into the substantially cylindrical shape then the bends 34define a first circular shape shown by dotted line 37 and the bends 35define a second circular shape shown by dotted line 39.

The embodiment of the stent 30 shown in FIGS. 4 to 6 has twelve struts32 and six bends 34, 35 between them and hence when formed intocylindrical or polygonal body 40 with an overlap of two struts has aplan view in the shape of a decagon as can be seen in FIG. 3.

When assembled onto a stent graft the stent is maintained into itscylindrical or polygonal body form by being stitched to the tubular bodyof the graft material.

FIG. 7 shows a connection socket of a stent graft incorporating a stentaccording to the present invention. The connection socket incorporatinga stent of this embodiment of the invention may be for a side arm for astent graft adapted for deployment into the common iliac artery or maybe for a terminal end of a leg of a bifurcated stent graft such as a fora stent graft adapted to be deployed into the aortic bifurcation.

In this embodiment the tube 50 may be a side arm for a stent graft ormay be a terminal end of a leg of a bifurcated graft. The tube 50 has asocket arrangement 52 into which may be placed a self-expanding stent, aballoon expandable stent or a composite stent or leg extension. The tube50 has a first ring 54 stitched to its terminal end and a second ring 56spaced apart from the first ring 54. Each ring 54 and 56 is formed fromat least two turns and preferably three turns of a nitinol wire and theends of the nitinol wire terminate in loops 58. The use of the loops 58prevent sharp ends from the NitinolJ wire from digging into thevasculature into which the stent graft is deployed.

Between the first ring 54 and the second ring 56 is a stent 60 accordingto the present invention formed from a resilient material. The stent 60is formed from a resilient wire such as nitinol wire or stainless steeland comprises a plurality of struts 62 with bends 64 between a pair ofstruts 62. The terminal struts 66 at each end terminate in a loop 68which comprises at least one turn of the resilient wire and preferablyone and a quarter turns. Stitching 70 is used to both hold the stentonto the tubular body 50 as well as to maintain the stent in itscylindrical or polygonal form.

The resilient stent 60 when stitched in its cylindrical or polygonalform is made to be of a size which is at rest slightly smaller than thediameter of the tube 50 and hence when sewn on to the outside of thetube 50 using stitching 70 it provides a diameter reducing effect on thetube 50.

When a balloon expandable stent or balloon expanded covered stent isplaced into the socket 52 and expanded the rings 54 and 56 provide firmlocking for the balloon expanded covered stent and the resilient stent60, which is expanded by the balloon expanded stent while it is beingballoon expanded, provides a compressive effect to keep tension on theballoon expanded stent. By this means a firm connection and an improvedseal can be obtained between a stent leg or arm and a bridging stent. Asimilar gripping effect can be obtained with the use of a self-expandingstent, a composite stent or other form of leg extension incorporation astent according to the present invention.

In one particular embodiment the side tube may have a diameter of 8 mmand hence a circumference of 26 mm. Each of the rings may have adiameter at rest of 7 mm and the resilient stent 60 when formed into itscylindrical or polygonal form may have a diameter at rest of 6 mm. Thefirst and second rings may be spaced apart by 10 mm and the length ofthe resilient stent 60 may be 6 mm. Hence there may be a gap between therings and the resilient stent of 2 mm.

In the case of a stent graft to be deployed into the common iliac arterywith the side arm adapted to extend towards the internal iliac arterythe side arm may have a diameter of 8 mm and a length after the join toa main stent graft of up to 25 mm. It will be realised that for stentgrafts to be deployed into the ascending or descending aorta with sidearms to extend into their respective branch vessels other lengths anddiameters will be applicable.

FIG. 8 shows a side branch stent graft or prosthesis of the type adaptedfor deployment into the iliac arteries, for instance, such that abridging stent can extend from the side arm into the internal iliac orhypogastric artery.

The stent graft 71 has a main tubular body 72 and a side arm 74. Boththe main tubular body and the side arm are formed from a seamless tubeof a biocompatible graft material such as Dacron. A triangular apertureis formed in the main tube and a bevel cut into the inner end of theside arm and the side arm stitched into the triangular aperture withstitching 78. The side arm has a connection socket arrangement 76 at itsdistal end 77. The connection socket arrangement 76 comprises a firstring 79 stitched to its terminal or distal end 77 and a second ring 80spaced apart from the first ring 79. Each ring 79 and 80 is formed fromat least two turns and preferably three turns of nitinol wire and theends of the nitinol wire terminate in loops 81. The use of the loops 81prevent sharp ends from the nitinol wire from digging into thevasculature into which the stent graft is deployed.

Between the first ring 79 and the second ring 80 is a stent 82 accordingto the present invention formed from a resilient material. The stent 82is formed from a resilient wire such as nitinol wire or stainless steeland comprises a plurality of struts with bends between a pair of struts.In this embodiment there are seven struts and six bends between them.The terminal struts at each end terminate in a loop 85 which comprisesat least one turn of the resilient wire and preferably one and a quarterturns. Stitching is used to both hold the stent onto the tubular body aswell as to maintain the stent in its cylindrical or polygonal form.

When a bridging stent such as a balloon expandable stent is placed intothe socket 77 as and expanded the rings 79 and 80 provide firm lockingfor the balloon expanded stent and the resilient stent 82 which isexpanded by the balloon expanded stent while it is being balloonexpanded provides a compressive effect to keep tension on the balloonexpanded stent. By this means a firm connection and an improved seal canbe obtained between the side arm and a bridging stent. A similargripping effect can be obtained with the use of a bridging stent in theform of a self-expanding stent, a composite stent or other form of legextension.

Throughout this specification various indications have been given as tothe scope of but the invention is not limited to any one of these butmay reside in two or more of these combined together. The examples aregiven for illustration only and not for limitation.

Throughout this specification and the claims that follow unless thecontext requires otherwise, the words ‘comprise’ and ‘include’ andvariations such as ‘comprising’ and ‘including’ will be understood toimply the inclusion of a stated integer or group of integers but not theexclusion of any other integer or group of integers.

What is claimed is:
 1. A stent graft comprising: a main body of graftmaterial having a side wall; a proximal end; a distal end; afenestration in the side wall; a side arm extending externally from thefenestration at an acute angle to the main body, the side arm comprisingtube of graft material having a proximal open end, a distal open end, adistal open end diameter, reinforcement about the distal open comprisingstitching, a first side, a second side and a front disposed opposite themain body, wherein the proximal open end is stitched to the main body atthe fenestration to form a main body/side arm junction; a plurality ofdiscrete stents along the length of the main body, wherein at least oneof the plurality of stents comprises an internal stent, and at leastanother stent comprises an external intermediate stent disposed aroundboth the main body and the side branch at the junction, wherein theintermediate stent comprises a zig zag stent having pairs of directlyadjacent struts with one pair of struts adjacent struts flanking thefront of the side arm, and wherein the distance between one pair ofdirectly adjacent struts is different than the distance between anotherpair of directly adjacent struts; a side arm stent disposed adjacent thedistal end of the side arm, the side arm stent having a diameter,wherein the diameter of the side arm stent is smaller than the diameterof the distal end of the side arm providing a compressive effect on thegraft material at the distal end of the side arm.
 2. The stent graft ofclaim 1, wherein the plurality of stents are self-expanding nitinolstents.
 3. The stent graft of claim 1, wherein the side arm furtherincludes a marker at the distal open end of the side arm.
 4. The stentgraft of claim 1, wherein the side arm stent is stitched to the side armsuch that it provides a diameter reducing effect to the graft materialof the side arm.
 5. A stent graft system comprising: a main body ofgraft material having a side wall; a proximal end; a distal end; afenestration in the side wall; a side arm extending externally from thefenestration at an acute angle to the main body, the side arm comprisingtube of graft material having a proximal open end, a distal open end, adistal open end diameter, reinforcement about the distal open comprisingstitching, a first side, a second side and a front disposed opposite themain body, wherein the proximal open end is stitched to the main body atthe fenestration to form a main body/side arm junction; a plurality ofdiscrete stents along the length of the main body, wherein at least oneof the plurality of stents comprises an internal stent, and at leastanother stent comprises an external intermediate stent disposed aroundboth the main body and the side branch at the junction, wherein theintermediate stent comprises a zig zag stent having pairs of directlyadjacent struts with one pair of struts adjacent struts flanking thefront of the side arm, and wherein the distance between one pair ofdirectly adjacent struts is different than the distance between anotherpair of directly adjacent struts; a side arm stent disposed adjacent thedistal end of the side arm, the side arm stent having a diameter,wherein the diameter of the side arm stent is smaller than the diameterof the distal end of the side arm providing a compressive effect on thegraft material at the distal end of the side arm; and a bridging stentconfigured to be received within the side arm.
 6. The stent graft systemof claim 5, wherein the bridging stent is a balloon expandable stent. 7.The stent graft system of claim 5, wherein the bridging stent isdisposed within the side arm and the side arm imposes a compressiveeffect on the bridging stent to provide tension on the bridging stent.8. The stent graft system of claim 5, wherein the bridging stent iscovered with graft material.
 9. The stent graft system of claim 5,wherein the side arm stent is stitched to the outside of the side armsuch that it provides a diameter reducing effect to the graft materialof the side arm.